Much like Spell Perfection, the following feats are meant for high level play.

I would like critiques on their balance (or lack there of), and am ultimately looking for ways to tighten up their wording so as to avoid possible abuse. In short, help me break them.

SPELLCASTING RESERVOIR
You have learned to increase the efficiency of your spellcasting so that you no longer exhaust your magical reserves when casting your weakest spells.
Prerequisites Must be a member of a spellcasting class with the cantrips or orisons class ability and that is capable of casting 9th-level spells, caster level 15
Benefit You may cast 1st-level spells as if they were cantrips or orisons, meaning they are not expended when cast and may be used again.
Normal Only 0-level spells can be cast without expending a spell slot.

IMPROVED SPELLCASTING RESERVOIR
You grow close to mastering basic spells, and you no longer exhaust your magical reserves when casting your lesser spells.
Prerequisites Spellcasting Resevoir, must be a member of a spellcasting class with the cantrips or orisons class ability and that is capable of casting 9th-level spells, caster level 17
Benefit You may cast 2nd-level spells as if they were cantrips or orisons, meaning they are not expended when cast and may be used again.
Normal Only 0-level spells can be cast without expending a spell slot.

GREATER SPELLCASTING RESERVOIR
You have become a master of efficiently drawing upon your magic to such an extent, that you no longer exhaust your magical reserves when casting basic spells.
Prerequisites Improved Spellcasting Resevoir, Spellcasting Resevoir, must be a member of a spellcasting class with the cantrips or orisons class ability and that is capable of casting 9th-level spells, caster level 19
Benefit You may cast 3rd-level spells as if they were cantrips or orisons, meaning they are not expended when cast and may be used again.
Normal Only 0-level spells can be cast without expending a spell slot.

Infinite summon monster 1 can give a level 2 souldrinker infinite money (summon a 2 HD monster, use the energy drain on it, repeat). The money can only be used for certain things, though.

Being able to cast lesser restoration at will would pretty much negate ability damage from the Blood Money spell, which lets you cast expensive stuff without any worries - including animate dead. You would have to multiclass for that, though.

There's a few immediate/swift action spells that would be spammed a lot (Grace and Gallant Inspiration are the first that come to mind). Prepared casters would get a lot of versatility for their lower level spells.

Borderline constant invisibility - which goes well with the summon monster spells and animate dead.

Fabricate Bullets at will would be a stupid way of getting infinite money.

I would compare with Spell Expertise. There are probably other ways these feats could be abused, but those are the first things I thought of.

Also, is it meant to work with people that multiclass? Like, 3 levels of divine casting and 17 levels of arcane would let you use the Improved Spellcasting Reservoir for both classes?

Scratch the gallant inspiration, being that it's a level 2 bard spell.

But, the other thing is buff spells like Resist Energy and Shield of Faith. Both of these scale with level, so you could use these feats to have basically a permanent +5 deflection AC and 30 energy resistance on the entire party. I know from experience that that can make things a little easier than they should be... because I like to break things...

Infinite summon monster 1 can give a level 2 souldrinker infinite money (summon a 2 HD monster, use the energy drain on it, repeat). The money can only be used for certain things, though.

Being able to cast lesser restoration at will would pretty much negate ability damage from the Blood Money spell, which lets you cast expensive stuff without any worries - including animate dead. You would have to multiclass for that, though.

There's a few immediate/swift action spells that would be spammed a lot (Grace and Gallant Inspiration are the first that come to mind). Prepared casters would get a lot of versatility for their lower level spells.

Borderline constant invisibility - which goes well with the summon monster spells and animate dead.

Fabricate Bullets at will would be a stupid way of getting infinite money.

I would compare with Spell Expertise. There are probably other ways these feats could be abused, but those are the first things I thought of.

Also, is it meant to work with people that multiclass? Like, 3 levels of divine casting and 17 levels of arcane would let you use the Improved Spellcasting Reservoir for both classes?

I have no idea what any of that is.

To answer your question, that is not the intent, no.

Drejk wrote:

Looks quite like Endless Power Archmage mythic path ability turned into a chain of non-mythic feats.

Infinite summon monster 1 can give a level 2 souldrinker infinite money (summon a 2 HD monster, use the energy drain on it, repeat). The money can only be used for certain things, though.

Being able to cast lesser restoration at will would pretty much negate ability damage from the Blood Money spell, which lets you cast expensive stuff without any worries - including animate dead. You would have to multiclass for that, though.

There's a few immediate/swift action spells that would be spammed a lot (Grace and Gallant Inspiration are the first that come to mind). Prepared casters would get a lot of versatility for their lower level spells.

Borderline constant invisibility - which goes well with the summon monster spells and animate dead.

Fabricate Bullets at will would be a stupid way of getting infinite money.

I would compare with Spell Expertise. There are probably other ways these feats could be abused, but those are the first things I thought of.

Also, is it meant to work with people that multiclass? Like, 3 levels of divine casting and 17 levels of arcane would let you use the Improved Spellcasting Reservoir for both classes?

I have no idea what any of that is.

To answer your question, that is not the intent, no.

Drejk wrote:

Looks quite like Endless Power Archmage mythic path ability turned into a chain of non-mythic feats.

What's that?

Fabricate Bullets allows you to craft 30 gp worth of firearm bullets at the cost of 2 gp. Even selling at half price, it's a net gain of 13 gp. It's a level 1 spell. If you can cast it as much as you want, you can earn a lot of money with it.

Vanish is the level 1 invisibility spell. I'm sure you can see how this would get used.

Blood Money lets you take 1 Str damage in exchange for 500 gp worth of material components for a spell. You can take as much strength damage as you want, so if you took 10 str damage you could cast a spell that would normall cost 5000 gp. Combined with lesser restoration gives you lots of expensive spells, but no single class has access to both of these spells, so it might not actually work. But, someone more creative than I might know another trick.

Souldrinker is a funky prestige class. It gets Energy Drain at level 2. When you use the Energy Drain ability (it's an at will ability) you get soul points. Soul points can be used for material components, crafting magic items, and a few other things. If you only have 2 levels in souldrinker, a 2 HD animal will give you 100 gp worth of souls to use in crafting or whatever. You can summon things with 2 HD with summon monster 1. So, you can summon a bunch of wimpy animals, energy drain them, and then use their souls for other stuff.

Grace is a swift action and lets you run around without provoking AoO. Good for clerics that need to reposition themselves.